The invention relates to a radial magnetic bearing for magnetic support of a rotor. Radial magnetic bearings are used for magnetically supporting rotors in a radial direction.
FIG. 1 shows a commercially-available radial magnetic bearing 1 in the form of a schematized cross-sectional view. The radial magnetic bearing 1 has a statically arranged stator 2. The stator 2 has a housing 3 and a stator element 4, which can consist for example of a filler material or of a number of metal sheets disposed behind one another in the axial direction X of the stator. The stator element 4 is magnetically-conducting and consists for example of a ferromagnetic material. The stator element 4 is disposed running around a rotor 5. The rotor 5 consists of a magnetically-conducting material such as a ferromagnetic material for example. The rotor 5 is rotationally fixed to a shaft 6. The shaft 6 can for example be a shaft of an electric motor or electric generator. The shaft 6 rotates in this case during operation of the electric motor or of the electric generator around the axis of rotation Z.
The radial magnetic bearing 1, on its side 12 of the stator element 4 facing towards the rotor 5, has recesses running in the axial direction X of the stator element 4, with only one recess 10 being labeled with a reference number in FIG. 1 for the sake of clarity. The recesses in this case are realized open on their side facing towards the rotor and thus in the shape of grooves. The recesses have a trapezoidal cross-section in such cases, as shown in the exemplary embodiment according to FIG. 1, which does not absolutely necessarily have to be the case. Electrical lines of coils run in the recesses, wherein, for the sake of clarity, only the lines 8a and 9a are provided with a reference number. The lines are disposed in the recesses. Teeth are formed by the recesses in the stator element 4, wherein, for reasons of clarity, only one tooth 18 is provided with a reference number. The coils in such cases are arranged around the teeth, wherein the current flows through the lines of the coils such that magnetic North pole N and magnetic South pole S are produced. The size of the teeth can be different in such cases, but this does not necessarily have to be the case, the teeth can also be the same size. Furthermore the number of teeth can differ from radial bearing to radial bearing.
In FIG. 2 the stator element 4 is shown with the coils running around the teeth in a simplified perspective view. For the sake of simplification in this case the number of recesses and thus the number of the teeth and coils are reduced and all teeth are shown as being identical in size. The same elements are provided in FIG. 2 with the same reference characters as in FIG. 1. For the sake of improved clarity only the two coils 8 and 9, as well as electric lines 8a and 9a of the coils 8 and 9 are provided with reference characters. The lines of the coils run in the recesses and around the teeth and thus form the teeth. The lines in such cases are usually present in the form of wrapping wires.
Returning to FIG. 1. Magnetic fields are created by the coils, which hold the rotor 5 suspended in an air gap 7 disposed between rotor 5 and stator 2. The coils are thus embodied for the creation of magnetic fields. To control the magnetic fields the radial magnetic bearing 1 has a control device 14, which activates, i.e. energizes, the coils accordingly to create the magnetic fields, this action being indicated by an arrow 15 in FIG. 1. The radial magnetic bearing 1 has sensors in such cases to detect the position of the rotor, which, for the sake of clarity, are not shown in FIG. 1 and which transfer to the control device 14 the position of the rotor in the air gap 7 for activation of the coils, this action being indicated in FIG. 1 by an arrow 16. The control device 14 contains regulation facilities for regulating the electrical currents passing through the coils. The radial magnetic bearing 1 is used for magnetic support of the rotor 5 and thus of the shaft 6 connected to the rotor 5 in the radial direction R. The radial magnetic bearing 1 is embodied for radial magnetic support of the rotor 5.
In commercially-available radial magnetic bearings the lines of the coils are disposed in such cases such that, in the recesses between the lines of the coils and the air gap 7 in each case, there remains a free space running in the axial direction X of the stator 2. For reasons of clarity only one free space 11 is labeled with a reference character in FIG. 1.
The rotor 5 generally consists of an electrically-conductive ferromagnetic material which experiences a force effect through the magnetic fields created by the stator. If the shaft 6 and thus the rotor 5 connected to the shaft are rotating in the air gap 7, the rotor 5 is subjected to a constant magnetic alternating field through the alternating magnetic poles N and S of the stator 2. Eddy currents are induced in the rotor 5 by this, which are undesired since they restrict the dynamics of the radial magnetic bearing and cause a thermal load to be imposed on the rotor. Since radial magnetic bearings are frequently used for applications in which the rotor is rotating at a high-speed, particular significance is attached to the reduction of the eddy currents in radial magnetic bearings.
In electrical engineering two measures are known in such cases for reducing eddy currents flowing in a rotor. A first option consists of reducing the number of magnetic poles of the stator. However this generally leads to a larger installation volume, so that a compromise must be found here between the smallest possible number of magnetic poles and a small installation volume. A further option consists of embodying the rotor from thin metal sheets which are isolated from one another.
Magnetic bearings for magnetic support of a rotor are known from U.S. Pat. No. 7,545,066 B2 and US 2010/0187926 A1.